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Modelling and analysis on high sediment concentration layer of fine sediments under wave-dominated conditions
Experiments and field observations have revealed that when silt and very fine sand are subject to oscillatory wave motion, a high shear flow layer and a high concentration layer (HCL) exist near the bottom. The behavior of the HCL is still under researched. Firstly, an intra-wave process based 1DV model was established for fine sediment transport under the combined action of waves and currents. Some key processes that were included in the model are represented through approaches for different bed forms (rippled bed and 'flat bed'), hindered settling, stratification, reference concentration and critical shear stress. A number of experimental datasets were collected to verify the model, which shows that the model is able to properly simulate the flow and sediment dynamics. Secondly, sensitivity analyses were carried out on some factors which would impact the suspended sediment concentration (SSC) profile of the HCL by the 1DV model, such as bed forms, flow dynamics, stratification effects, mobile bed effects and hindered settling. Results show that bed forms play a significant role in the HCL and determination of the shape of the concentration profile. When a current is imposed, the SSC profiles become smoother; however, sediment concentration in the lower HCL is still dominated by the wave motions. For finer sediment, the stratification effects and the mobile bed effects strongly impact the HCL. In conclusion, this paper provides a tool for the study of the HCL and an evaluation of several impact factors on the HCL.
Silicone-water partition coefficients determined by cosolvent method for chlorinated pesticides, musks, organo phosphates, phthalates and more
To further support implementation of monitoring by passive sampling, robust sampler-water partition coefficients (Kpw) are required to convert data from passive sampler into aqueous phase concentrations. In this work silicone-water partition coefficients were determined for ~80 hydrophobic organic contaminants using the cosolvent method. Partition coefficients (Kpm) were measured in pure water and water-methanol mixtures up to a methanol mole fraction of 0.3 (50% v/v). Subsequently, logKpw in pure water was determined as the intercept of linear regression of the logKpm with the corresponding methanol mole fractions. LogKpw were determined for phthalates, musks, organo phosphorus flame-retardants, chlorobenzenes, pesticides, some PCBs and a number of miscellaneous compounds. The median standard error and 95% confidence interval of the measured logKpw was 0.06 and 0.13, respectively. The overall relationship between Kpw and Kow seems insufficient to predict Kpw for unknown compounds. Prediction may work within a group of compounds with similar nature, e.g. homologues but HCH isomers having the same Kow exhibit Kpw ranging over an order of magnitude. Long alkyl-chain phthalates and tris(2-ethylhexyl) phosphate; all having a molecular volume >400 A3, deviated the most from the Kpw-Kow relationship.
Dependence between high sea-level and high river discharge increases flood hazard in global deltas and estuaries
When river and coastal floods coincide, their impacts are often worse than when they occur in isolation; such floods are examples of 'compound events'. To better understand the impacts of these compound events, we require an improved understanding of the dependence between coastal and river flooding on a global scale. Therefore, in this letter, we: provide the first assessment and mapping of the dependence between observed high sea-levels and high river discharge for deltas and estuaries around the globe; and demonstrate how this dependence may influence the joint probability of floods exceeding both the design discharge and design sea-level. The research was carried out by analysing the statistical dependence between observed sea-levels (and skew surge) from the GESLA-2 dataset, and river discharge using gauged data from the Global Runoff Data Centre, for 187 combinations of stations across the globe. Dependence was assessed using Kendall's rank correlation coefficient (τ) and copula models. We find significant dependence for skew surge conditional on annual maximum discharge at 22% of the stations studied, and for discharge conditional on annual maximum skew surge at 36% of the stations studied. Allowing a time-lag between the two variables up to 5 days, we find significant dependence for skew surge conditional on annual maximum discharge at 56% of stations, and for discharge conditional on annual maximum skew surge at 54% of stations. Using copula models, we show that the joint exceedance probability of events in which both the design discharge and design sea-level are exceeded can be several magnitudes higher when the dependence is considered, compared to when independence is assumed. We discuss several implications, showing that flood risk assessments in these regions should correctly account for these joint exceedance probabilities.
The interaction of a lock’s filling jet and the ship in the lock chamber, using scale model measurements
In the design of shipping locks, an accurate prediction of the force on a vessel during levelling is required to ensure a safe but swift operation of the future lock. This force is often predicted by distinguishing several force mechanisms of which the translatory wave, filling jet and density current are generally most important. The present study focusses on the interaction of the filling jet with the ship and aims at understanding how the ship changes the flow pattern and how, consequently, this flow results in a force on the ship. To this end, scale model measurements are performed in a flume with a schematized lock and ship geometry. In addition to measuring the forces on the ship, the flow pattern has been measured using PIV (particle image velocimetry) measurements. The results present a detailed view of the flow pattern in the ship’s vicinity. The measured forces are compared to Lockfill and show good agreement despite the simplifications that have been made.
ISHS 2018 : proceedings of the 7th International Symposium on Hydraulic Structures (Aachen, Germany, 15-18 May 2018)
The impacts of recent drought on fire, forest loss, and regional smoke emissions in lowland Bolivia
In the southern Amazon relationships have been established among drought, human activities that cause forest loss, fire, and smoke emissions. We explore the impacts of recent drought on fire, forest loss, and atmospheric visibility in lowland Bolivia. To assess human influence on fire, we consider climate, fire, and vegetation dynamics in an area largely excluded from human activities since 1979, Noel Kempff Mercado National Park (NK) in northeastern Bolivia. We use data from five sources: the Moderate Resolution Imaging Spectroradiometer Collection 6 active fire product (2001–2015) (MODIS C6), Global Fire WEather Database (GFWED) data (1982–2015), MODIS land cover data (2001–2010), MODIS forest loss data (2000–2012), and the regional extinction coefficient for the southwestern Amazon (i.e., B ext), which is derived from horizontal visibility data from surface stations at the World Meteorological Organization (WMO) level (1973–2015). The B ext is affected by smoke and acts as a proxy for visibility and regional fire emissions. In lowland Bolivia from 2001 to 2015, interannual Drought Code (DC) variability was linked to fire activity, while from 1982 to 2015, interannual DC variability was linked to Bext. From 2001 to 2015, the B ext and MODIS C6 active fire data for lowland Bolivia captured fire seasonality, and covaried between low- and high-fire years. Consistent with previous studies, our results suggest B ext can be used as a longer-term proxy of regional fire emissions in southwestern Amazonia. Overall, our study found drought conditions were the dominant control on interannual fire variability in lowland Bolivia, and fires within NK were limited to the Cerrado and seasonally inundated wetland biomes. Our results suggest lowland Bolivian tropical forests were susceptible to human activities that may have amplified fire during drought. Human activities and drought need to be considered in future projections of southern Amazonian fire, in regard to carbon emissions and global climate.
Fit for purpose? : building and evaluating a fast, integrated model for exploring water policy pathways
Exploring adaptation pathways is an emerging approach for supporting decision making under uncertain changing conditions. An adaptation pathway is a sequence of policy actions to reach specified objectives. To develop adaptation pathways, interactions between environment and policy response need to be analysed over time for an ensemble of plausible futures. A fast, integrated model can facilitate this. Here, we describe the development and evaluation of such a model, an Integrated Assessment Metamodel (IAMM), to explore adaptation pathways in the Rhine delta for a decision problem currently faced by the Dutch Government. The theory-motivated metamodel is a simplified physically based model. Closed questions reflecting the required accuracy were used to evaluate the model's fitness. The results show that such a model fits the purpose of screening and ranking of policy options and pathways to support the strategic decision making. A complex model can subsequently be used to obtain more detailed information.
Unravelling the myth : the use of Decisions Support Systems in marine management
Over the past decade the development of Decision Support Systems (DSSs) for the management of seas and oceans has increased rapidly. These DSSs take many shapes and forms and their application in actual decision processes varies widely. In order to appreciate the multitude of DSSs a theoretical framework was developed to evaluate the appropriateness of a given DSS for marine management decision processes with the aim to guide developers in building better DSSs. This framework was applied to a number of DSSs recently developed for marine management. Many tools, promoted to be DSSs, are in fact science driven models that do not address the basic problems and challenges of decision making. Of course, by providing information and making scientific data available in order to make scientifically informed decisions, science does have a role in environmental and ecosystem based decision making, yet the contribution of science to decision making in marine management by these models is highly overrated. In order for a DSS to be relevant and useful it must be aligned with the needs of the decision maker and provide available data in such a way that it becomes information in the decision process. The framework used to evaluate the DSSs can be a helpful tool to apply throughout the development of a DSS in order to enhance the effectiveness/usefulness of these tools through the engagement of end-users and stakeholders.
Modelling soil-water interaction with the Material Point Method : evaluation of single-point and double-point formulations
Many problems in geotechnical engineering involve large deformations and soil-water inter-actions, which pose challenging issues in computational geomechanics. In the last decade, the Material Point Method (MPM) has been successfully applied in a number of large-deformation geotechnical problems and multiphase MPM formulations have been recently proposed. In particular, there exist two advanced coupled hydro-mechanical MPM approaches to model the interaction between solid grains and pore fluids: the single-point and the double-point formulation. The first discretizes the soil-water mixture with a single set of material points (MP) which moves according to the solid velocity field. The latter uses two sets of MP, one for the fluid phase and the other for the solid phase and they move according to the respective velocity field. The aims of this work is to present and compare the two theories, to emphasize their limitations and potentialities, and to discuss their applicability in the geotechnical field. To this end, the results of two numerical examples carried out by using both formulations are presented: a 1D-consolidation problem and a saturated column collapse problem.
Numerical Methods in Geotechnical Engineering IX : proceedings of the 9th European Conference on Numerical Methods in Geotechnical Engineering - NUMGE 2018 (June 25-27, 2018, Porto, Portugal)